1. Field of the Disclosure
The present invention relates to a semiconductor device, more particularly, to an image sensor of a semiconductor device and a method of manufacturing the same.
2. Discussion of the Related Art
In general, image sensors are semiconductor devices that convert optical images into electrical signals.
An image sensor may be classified as a charge coupled device (CCD) image sensor or as a complementary metal oxide semiconductor (CMOS) image sensor.
CMOS image sensors include an integer multiple number of MOS transistors as the number of pixels. Using CMOS technology, a control circuit can be simultaneously integrated with signal processing circuits, which are peripheral circuits. Then, the CMOS image sensor switches to detect outputs.
Each CMOS image sensor pixel includes a photodiode and a plurality of MOS transistors, and it typically converts a light incident on an image sensor chip into an electrical signal.
In recent years, vertical image sensors have been developed and widely used. The vertical photodiodes provide the advantage of having a vertical photodiode that is able to detect various colors with a single pixel, in contrast to a horizontal image sensor structure.
A conventional CMOS image sensor is manufactured according to a following method.
At least one photodiode is formed on a substrate and a multilayered interlayer dielectric layer having metal lines therein is formed on the substrate having the photo diode formed thereon.
An oxide or nitride is then deposited on the interlayer dielectric layer to form a passivation layer. After at least one color filter layer corresponding to the photodiode is formed on the passivation layer, at least one microlens is formed on or over the color filter layer. The image sensor may also include a planarizing layer formed on or over the passivation layer.
The passivation layer of the image sensor manufactured through the conventional process described above is formed with substantially the same thickness in every pixel.
FIG. 1 is a diagram illustrating light incident on the conventional image sensor, as described above. FIGS. 2A and 2B are graphs illustrating profiles of an electric field and light intensity of the light incident on the conventional image sensor, respectively.
The size of image sensors, including the pixels, is progressively shrinking in the ULSI era. If the passivation layer is formed in every pixel with the identical thickness, as in the conventional image sensor, the phase of the light reaching the photodiodes of each pixel is identical.
That is, as shown in the profile of the electric field of FIG. 2A, light incident on neighboring pixels in the conventional image sensor have identical phases. As a result constructive interference of light between neighboring pixels occurs, as shown in the profile of the light intensity. The resulting constructive interference results in cross-talk between adjacent pixels, distorting the image data received by the image sensor. Specifically, diffraction of the incident light deteriorates and/or distorts the profile of the light intensity, as shown in FIG. 2B. This phenomenon is especially pronounced in image sensors where the size or width of the light beam focused on the photodiode is larger than the size of the photodiode.
The cross talk of image data has become a problem as image sensor technology has become progressively miniaturized, resulting in smaller sized pixels and photodiodes. This phenomenon reduces the quality of the images produced by the image sensor.